Research proposed for the coming year will be carried out in three areas of cellular and comparative physiology. Basic transport processes involved in intracellular osmoregulation will be examined. The volume and composition of extracellular fluid will be perturbed in certain euryhaline elasmobranchs that exhibit changes of 20-30% in plasma osmotic pressure after transfer from full strength to half-strength seawater. Modifications will then be noted in intracellular contents of urea, trimethylamine oxide, amino acids and electrolytes as various tissues cope with adaptive changes occurring in the osmolarity of blood and interstitial fluid in animals thus exposed to environmental osmotic stress. Active transport processes that underlie the transcellular movement of strong electrolytes will be identified in the renal tubule, collecting ducts, ureter and urinary bladder of the aglomerular stenohaline marine teleost, Lophius (goosefish). Renal hemodynamic studies are directed mainly at characterizing the reflex renal shutdown that accompanies bradycardia in rabbits undergoing "voluntary" apnea. Cholinergic vs adrenergic components of motor pathways that simultaneously reduce cardiac output and also cause intense generalized peripheral vasoconstriction are being identified.